NEW YORK (AP) -- Boeing's much-delayed 787 Dreamliner has hit another production snafu.

Hairline cracks have been discovered in the wings of some 787s that are being built. The Chicago-based manufacturer says none of the 122 jets already flown by airlines around the world are affected.

"We are confident that the condition does not exist in the in-service fleet," Boeing spokesman Doug Alder said in an email. "We understand the issue, what must be done to correct it and are completing inspections of potentially affected airplanes."

Boeing says that roughly 40 airplanes might be affected and that it will take one to two weeks to fix the cracks found on shear ties on a wing rib.